Sheet feeding device and image forming apparatus

ABSTRACT

A sheet feeding device includes: a sheet storage unit that stores a sheet stack of a plurality of sheets; and a plurality of nozzles configured to generate air currents blown out to the sheet stack, the air currents separate an uppermost sheet from the rest of stack of the plurality of sheets including a next sheet, the next sheet being situated immediately below the uppermost sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2010-267569 filed in Japan on Nov. 30, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to sheet feeding devices and image forming apparatuses. More particularly, the invention relates to a sheet feeding device that separates an uppermost sheet from a stack of sheets of paper placed in a sheet storage unit and conveys the uppermost sheet, and an image forming apparatus including the sheet feeding device.

2. Description of the Related Art

An image forming apparatus of various types, such as an electrophotographic copier, printer, or facsimile, or an inkjet printer, generally includes a sheet feeding device that picks up sheets one by one from a sheet storage unit, on which a stack of a plurality of sheets of paper is placed, and feeds the picked-up sheet to an image forming unit, or a printing unit.

In recent years, with an increasing diversity of paper type, sheets of various types of paper other than plain paper, such as coated paper, art paper, and films, are used in image forming. However, such sheets of various types of paper other than plain paper generally have properties of highly-smooth surfaces and low air permeability, and are hydroscopic. These properties generally enhance inter-sheet adhesion of the sheets. Accordingly, these sheets have a problem of being hard to separate from each other as compared with sheets of plain paper and likely to cause multiple-sheet-feeding-at-a-time or failure to feed a sheet to occur.

Sheets having such properties as described above are generally fed by using, as is the case with printers, a pneumatic sheet feeding device that utilizes a suction cup, or a sheet suction device that includes a belt-like feeding roller and utilizes negative pressure created by blowing air.

To solve the problem described above, a sheet feeding device that includes a nozzle, mounted on an upper portion of a guide member, to blow air supplied from an air sending device including a blower and the like onto an end face of a top portion of a stack of the sheets is proposed. The guide member is configured to restrict a side-end position or a trailing-end position of sheets. (see, for example, Japanese Patent Application Laid-open No. 2005-001855, Japanese Patent No. 4095656, or Japanese Patent Application Laid-open No. 2007-223700).

In each of the sheet feeding device disclosed in Japanese Patent No. 4095656 and that disclosed in Japanese Patent Application Laid-open No. 2007-223700, a sheet retainer that controls a height of a sheet being lifted, is provided above the nozzle which blows out air. The sheet retainer is provided to control a position of a top surface of the lifted-up sheet so that the air blown from the nozzle mounted on an end face of the guide section reliably hits the end face of the top portion of the sheet. Thus the sheets are efficiently separated.

However, the sheet feeding devices disclosed in Japanese Patent Application Laid-open No. 2005-001855, Japanese Patent No. 4095656, and Japanese Patent Application Laid-open No. 2007-223700 still have a problem of not completely being capable of preventing multiple sheets sticking to each other and being fed at a time from occurring.

In each of the sheet feeding device disclosed in Japanese Patent No. 4095656 and that disclosed in Japanese Patent Application Laid-open No. 2007-223700, the sheet retainer is in constant contact with a sheet while the sheet is being fed with air being blown onto the sheet. Accordingly, the sheet retainer itself can be undesirably worn. Furthermore, friction between the sheet retainer and the sheet may produce a streak-like scratch on the sheet. The scratch can degrade image quality seriously especially in a case when the sheet is coated paper having a glossy surface.

Furthermore, the sheet retainer is arranged to constantly protrude from a side fence. Accordingly, a sheet may be caught by the sheet retainer at times when the sheet is loaded onto a tray or the like. This impairs operability, which is also a problem.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve the problems in the conventional technology.

According to an aspect of the present invention, a sheet feeding device includes: a sheet storage unit that stores a sheet stack of a plurality of sheets; and a plurality of nozzles configured to generate air currents blown out to the sheet stack, the air currents separate an uppermost sheet from the rest of stack of the plurality of sheets including a next sheet, the next sheet being situated immediately below the uppermost sheet.

According to another aspect of the present invention, an image forming apparatus includes: the above described sheet feeding device; and an image forming unit that forms an image on the sheet.

The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an image forming apparatus, to which a first embodiment of the present invention is applied;

FIG. 2 is a perspective view illustrating a sheet feeding device according to the first embodiment;

FIG. 3 is a perspective view illustrating the sheet feeding device as viewed from a lateral direction with respect to a sheet feeding direction;

FIG. 4 is a schematic diagram illustrating a state when the sheet feeding device is sending air;

FIG. 5 is a cross-sectional view illustrating a state when the sheet feeding device is sending air;

FIG. 6 is a schematic diagram illustrating a state when a sheet feeding device according to a second embodiment of the present invention is sending air;

FIG. 7 is a schematic diagram illustrating a state when a sheet feeding device according to a third embodiment of the present invention is sending air;

FIG. 8 is a schematic diagram illustrating a state when the sheet feeding device is changing air-flow rates;

FIG. 9 is another schematic diagram illustrating a state when the sheet feeding device is changing the airflow rates;

FIG. 10 is a perspective view illustrating a sheet feeding device according to a fourth embodiment of the present invention;

FIG. 11 is an elevational view illustrating a state of an arrangement of nozzles of the sheet feeding device;

FIG. 12 is an elevational view illustrating how separating air of the sheet feeding device acts; and

FIG. 13 is a schematic diagram illustrating a state when the sheet feeding device is separating a sheet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Each of sheet feeding devices according to embodiments of the present invention is a sheet feeding device that separates an uppermost sheet from a stack of a plurality of sheets of paper placed in a sheet storage unit of an image forming apparatus and conveys the uppermost sheet. The sheet feeding device includes a plurality of nozzles which: blows out air currents against the sheet stack; and generates air currents that separate a next sheet positioned immediately below the uppermost sheet from the uppermost sheet. The next sheet receives, at its upper surface, the air currents from an air-current generating device such that the next sheet is pressed down by the air currents. Accordingly, multiple-sheet-feeding-at-a-time is reliably prevented.

Embodiments

Image forming apparatuses according to embodiments of the present invention (hereinafter, simply referred to as “embodiment(s)”) will be described below. Although several examples are described below as the embodiments, it should be noted that the present invention is not limited to those specific embodiments described below, and numerous improvements, changes, modifications, alterations, and application examples would occur to those skilled in the art without departing from the scope of the present invention.

First Embodiment

An image forming apparatus according to a first embodiment will be described first. FIG. 1 is a schematic diagram illustrating an image forming apparatus 11 to which the first embodiment is applied. FIG. 2 is a perspective view illustrating an internal structure of a sheet feeding device 13 according to the first embodiment. As illustrated in FIG. 1, the image forming apparatus 11 includes an image forming apparatus main body 12 and the sheet feeding device 13 connected to one side surface of the image forming apparatus main body 12. The image forming apparatus main body 12 includes an image forming unit of an electrophotographic, inkjet, or the like method that forms an image on a sheet fed by the sheet feeding device 13. The sheet feeding device 13 separates a sheet of a designated size, one by one, from stacks of sheets of different sizes placed inside the sheet feeding device 13 and conveys the sheet to the image forming apparatus main body 12.

As illustrated in FIG. 2, the sheet feeding device 13 includes: a sheet feeding tray (sheet storage unit) 21 that includes a bottom plate 6, on which a stack of a plurality of sheets of paper is placed; and a suction belt unit (sheet feeder) 22 that picks up sheets of an uppermost portion of the sheet stack one by one and feeds the sheet to the image forming apparatus main body 12.

Side fences 23 that guide side surfaces, with respect to a width direction (direction orthogonal to a sheet feeding direction), of the sheet stack placed on the bottom plate 6 are provided at two inner ends of the sheet feeding tray 21. An end fence 10 that presses a trailing-end surface of the sheet stack is provided in the sheet feeding tray 21 at a position to the rear of the sheet stack.

The sheet feeding device 13 according to the first embodiment performs sheet separation by sending air to the sheet stack. FIG. 3 is a perspective view illustrating the sheet feeding device according to the first embodiment as viewed from a lateral direction with respect to the sheet feeding direction. FIG. 4 is a schematic diagram illustrating a state the sheet feeding device is sending air. FIG. 5 is a cross-sectional view illustrating a state when the sheet feeding device is sending air. FIGS. 3 to 5 illustrate a state when the suction belt unit 22 is removed from the sheet feeding device 13. The sheet feeding device 13 includes lifting-air blowers 1 for use in sheet lifting immediately below the suction belt unit 22. The lifting-air blowers 1 are used to lift up an uppermost sheet of a sheet stack 100 so that the suction belt unit 22 can convey the uppermost sheet.

Each of the side fences 23 includes a separating-air nozzle 24. Air for use in the sheet separation (hereinafter, “separating air”) is blown from the separating-air nozzles 24 against side surfaces of the sheet stack. A blowing-down-air nozzle 25 is also provided above the separating-air nozzle 24. Blown-down air is blown onto a top surface of a next sheet 102, which is a sheet immediately below the uppermost sheet of the sheet stack 100, from the blowing-down-air nozzles 25 situated diagonally above the top surface.

As illustrated in FIG. 4, each of the separating-air nozzles 24 is connected to a separating-air blower 26. Air currents, serving as the separating air, generated by the separating-air blowers 26 are blown through the separating-air nozzles 24 against side portions of sheets. Each of the blowing-down-air nozzles 25 is connected to a blowing-down-air blower 27. Air currents, serving as the blowing-down air, generated by the blowing-down-air blowers 27 are blown through the blowing-down-air nozzles 25 onto the sheets. Each of the blowers 26 and 27 includes a motor as a drive source, and a fan that is rotary driven by the motor to generate the air currents.

Note that, when airs are sent from the nozzles 24 and 25, the uppermost sheet of the sheet stack 100 is in state of being conveyed by the suction belt unit 22, although not illustrated in FIGS. 3 to 5. Also note that blowing air from the blowing-down-air nozzles 25 is performed concurrently with blowing air from the separating-air nozzles 24 that are performing sheet feeding.

As illustrated in FIGS. 4 and 5, the blowing-down air from the blowing-down-air nozzles 25 presses down the top surface of the next sheet 102 that is lifted by the separating air from the separating-air nozzles 24, thereby preventing the next sheet 102 from being lifted too high. This makes it possible to maintain a height of the end face of the sheet at a position of the separating-air nozzles 24 appropriately, and to perform the sheet separation satisfactorily. During this operation, no damage is inflicted on the sheet and therefore no degradation in image occurs because nothing comes into contact with a to-be-printed surface of the sheet. Furthermore, there is no possibility that the sheet would be caught because nothing protrudes from the side fences 23. Accordingly, operability of loading sheets is considerably increased.

Meanwhile, sheet adhesion strength varies greatly depending on a sheet type, sheet thickness, sheet size, and environment. More specifically, coated paper, thick paper, large-sized paper, and paper in an environment of high humidity and high temperature respectively has larger adhesion strength than that of plain paper, thin paper, small-sized paper, and paper in an environment of low humidity and low temperature.

In view of this, in the first embodiment, a separating-air controller 51 can drive control the separating-air blower 26. In a situation where sheets stick to each other with relatively large adhesion strength, the separating-air controller 51 intensifies strength of the separating air blown from the separating-air nozzles 24 automatically or manually. The separating-air controller 51 controls, more specifically, the number of revolutions of the motors that drive the separating-air blowers 26.

As described above, the stronger the wind power of the separating air is, the higher the sheet is lifted. In view of this, it is necessary to control the wind power of the blowing-down air from the blowing-down-air nozzles 25 in order to prevent an excessive lifting of the sheet and adjust the height of the sheet to an appropriate level. For this purpose, a blowing-down-air controller 52 that controls the wind power of the blowing-down air from the blowing-down-air nozzles 25 may be provided. The blowing-down-air controller 52 controls the number of revolutions of the motors that drive the blowing-down-air blowers 27. By this control, in a condition where the wind intensity of the separating air from the separating-air nozzles 24 is relatively high, the amount of the blowing-down air may be increased to suppress the excessive lifting of the sheet.

As described above, in the first embodiment, the amount of the blowing-down air to be blown is adjustable depending on a condition related to the separating air. Accordingly, the height of the sheet may be constantly maintained at an appropriate level, thus the sheet separation may be performed satisfactorily.

Meanwhile, in the first embodiment, the amount of the blowing-down air is controlled to increase in accordance with increase of the amount of the separating air. A lifting height of the sheet itself may be detected with a sensor or the like, and the wind power of the blowing-down air may be intensified when the height of the top surface of the sheet exceeds a predetermined value.

Second Embodiment

A second embodiment will be described below. FIG. 6 is a schematic diagram illustrating a state when a sheet feeding device according to the second embodiment is sending air. In the second embodiment, a common blower 41 is arranged to send air to the separating-air nozzles 24 and also to the blowing-down-air nozzles 25. A duct extending from the blower 41 is divided into a separating-air duct 42 and a blowing-down-air duct 43 so that airs can be blown out from the nozzles 24 and 25.

According to the second embodiment, only a single blower is used to send air to each of the nozzles. Accordingly, the number of parts can be reduced, and hence cost reduction, reduction in power consumption, and reduction in man-hours necessary to perform assembly may be achieved.

Third Embodiment

A third embodiment will be described below. FIG. 7 is a schematic diagram illustrating a state when a sheet feeding device according to the third embodiment is sending air. FIGS. 8 and 9 are schematic diagrams illustrating states when the sheet feeding device has changed the amount of the sending air. In the third embodiment, a flow-rate adjusting plate 28, of which mounting angle is changeable by pivoting about a pivot point 28 a, is provided at a branch portion between the separating-air duct 42 and the blowing-down-air duct 43 described above in the second embodiment. The flow-rate adjusting plate 28 is driven by a driver (not shown), such as a motor or an electromagnetic solenoid. A controller (not shown) controls driving of the driver to thereby control the angle of the flow-rate adjusting plate 28.

In the third embodiment, a ratio between the separating air and the blowing-down air can be changed as in the first embodiment by changing the angle of the flow-rate adjusting plate 28. For example, in a situation where the sheet is lifted insufficiently and does not reach an appropriate height because the wind power of the blowing-down air is too strong, as illustrated in FIG. 8, the ratio of the airflow rate of the blowing-down air may be reduced by tilting the flow-rate adjusting plate 28 toward the blowing-down-air duct 43.

In contrast, in a situation where the sheet is lifted too high because the wind power of the separating air is too strong, as illustrated in FIG. 9, the ratio of the airflow rate of the separating air may be reduced by tilting the flow-rate adjusting plate 28 to pivot toward the separating-air duct 42, in a direction of reducing the airflow rate of the separating air.

According to the third embodiment, the ratio between the separating air amount and the blowing-down air amount can be adjusted by tilting the flow-rate adjusting plate 28 depending on a condition of the separating air. Accordingly, the height of the sheet can be constantly maintained at an appropriate level, and thus the sheet separation can be satisfactorily performed.

Meanwhile, in the first embodiment and the third embodiment, operations of the separating-air blowers 26, the blowing-down-air blowers 27, and the flow-rate adjusting plate 28 are controllable from an operating unit of the sheet feeding device or an operating unit of the image forming apparatus. This configuration allows a user to adjust the airflow rate of each of the separating air and the blowing-down air without disassembling the sheet feeding device or the like. Accordingly, labor for running the image forming apparatus can be significantly reduced.

The image forming apparatus provided with any one of the preceding sheet feeding devices does not cause image degradation resulting from a scratch on a sheet or the like to occur even when pneumatic sheet separation is performed. Furthermore, user-friendliness for loading sheets improves, thus quality of the image forming apparatus as equipment improves.

As described above, the image forming apparatus according to any one of the first to third embodiments is capable of preventing a sheet from being lifted too high by the blowing-down air blown from the blowing-down-air nozzles so as to press a top surface of a sheet lifted by the separating air. Accordingly, a height of an end face of the sheet can be maintained at the level of the separating-air nozzles appropriately, and thus sheet separation can be performed satisfactorily. During this operation, no damage is inflicted to the sheet and therefore no degradation in image occurs because nothing comes into contact with a to-be-printed surface of the sheet. Furthermore, there is no possibility that the sheet would be caught because nothing protrudes from the side fences. Accordingly, user-friendliness for loading sheets is considerably increased.

Fourth Embodiment

A sheet feeding device according to a fourth embodiment will be described below. FIG. 10 is a perspective view illustrating the sheet feeding device according to the fourth embodiment. FIG. 11 is an elevational view illustrating an arrangement of nozzles of the sheet feeding device. FIG. 12 is an elevational view illustrating how air sent from the sheet feeding device acts. FIG. 13 is another schematic diagram illustrating a state when the sheet feeding device is separating a sheet.

In the fourth embodiment, the sheet stack 100 is placed on a sheet feeding table 82 as illustrated in FIG. 10. The sheet feeding table 82 is movable up and down by a hoisting and lowering mechanism (not shown). The sheet stack 100 placed on the sheet feeding table 82 is positioned, in a width direction that is rectangular to a sheet feeding direction, by side fences 83 (only one of which is illustrated in FIG. 10). In a length direction that is along the sheet feeding direction, the sheet stack 100 is positioned at its leading end by a leading-end guide plate 81 and at its trailing end by an end fence 84. Thus, the sheet stack 100 is maintained in a state of being free from skew. A sheet feeding device 80 is provided to separate an uppermost sheet 101 from the sheet stack 100 and conveys the uppermost sheet 101.

The sheet feeding device 80 includes a suction belt unit 60 arranged above the sheet stack 100 placed on the sheet feeding table 82, and an air sending device 70 arranged on a side where the leading-end guide plate 81 is provided relative to the sheet stack 100. The suction belt unit 60 includes an endless sheet feeding belt 61 wound around a drive roller 62 and a driven roller 63, and a negative pressure air chamber 65 that holds a negative pressure therein. The drive roller 62 is rotary driven by a drive shaft 64. The negative pressure air chamber 65 is arranged inside a loop of the sheet feeding belt 61. The negative pressure air chamber 65 sucks the uppermost sheet 101 lifted by the air sending device 70 at a suction hole opened in the sheet feeding belt 61.

The air sending device 70 includes: an air chamber 71 that holds compressed air therein; and two types of nozzles connected to the air chamber 71 including a lifting-air nozzles 72 that blows out the lifting air and separating-air nozzles 73 that generates separating air. As illustrated in FIG. 11, two pieces of the lifting-air nozzles 72 apart from each other are provided in the air chamber 71; and three pieces of the separating-air nozzles 73 are provided between the lifting-air nozzles 72.

As illustrated in FIG. 12, the separating-air nozzles 73 are composed of: separating-air nozzles 73 a and 73 b arranged at two ends; and a separating-air nozzle 73 c arranged at a center between the separating-air nozzles 73 a and 73 b. Separating airs from the separating-air nozzles 73 a and 73 b at the two ends are directed toward inside of a surface of the sheet feeding belt 61 in its width direction and against a conveying direction of the sheet feeding belt 61. Separating air from the center separating-air nozzle 73 c is directed in a direction substantially perpendicular to the width direction of the sheet feeding belt 61 and against the conveying direction of the sheet feeding belt.

The separating airs jetted from the three separating-air nozzles 73 a, 73 b, and 73 c hit the sheet feeding belt 61 as illustrated in FIG. 12 and flow along the sheet feeding belt 61, or the uppermost sheet 101 being conveyed by the sheet feeding belt 61, and merge together. The directions of the separating airs are thus changed from horizontal directions to a downward direction. The separating airs press down the next sheet 102 and a second next sheet 103, separating the sheets 102 and 103 from the uppermost sheet 101.

In the fourth embodiment, the sheet stack 100 is separated by the lifting airs from the lifting-air nozzles 72. The lifted uppermost sheet 101 is sucked to the sheet feeding belt 61 by the negative pressure air chamber 65. When, in this state, the separating airs are jetted from the separating-air nozzles 73, as described above, the separating airs flow along the uppermost sheet 101 and then downward to hit, together with the lifting air, a top surface of the next sheet 102 arranged below the uppermost sheet 101, thereby pressing down the next sheet 102. The separating airs and the lifting airs from the lifting-air nozzles 72 also flow, together with the lifting airs, to a portion below the next sheet 102 to press down the sheet 103 located further below the next sheet 102, thereby separating each of the sheets 102 and 103. Thus, the uppermost sheet 101 is reliably separated from the sheets 102 and 103 and conveyed by the sheet feeding belt 61 one by one.

Meanwhile, when the airs to be blown from the nozzles are warm air, dehumidification of the sheet is additionally performed. Accordingly, the sheet separation can be performed more effectively.

According to an aspect of the present invention, air currents press down a top surface of a next sheet that is situated immediately below the uppermost sheet. Accordingly, not only multiple-sheet-feeding-at-a-time is reliably prevented but also impairment of ease of loading sheets is prevented. Furthermore, image degradation resulting from a scratch on a sheet or the like can be prevented.

Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth. 

1. A sheet feeding device comprising: a, sheet storage unit that stores a sheet stack of a plurality of sheets; and a plurality of nozzles configured to generate air currents blown out to the sheet stack, the air currents separate an uppermost sheet from the rest of stack of the plurality of sheets including a next sheet, the next sheet being situated immediately below the uppermost sheet.
 2. The sheet feeding device according to claim 1, wherein the plurality of nozzles is configured to generate: a first air current that is blown against a side surface of the sheet stack to separate the sheets of the sheet stack; and a second air current that is blown onto a top surface of the next sheet to press down the next sheet.
 3. The sheet feeding device according to claim 2, wherein the second air current is generated from a second nozzle that includes a leading end directed obliquely downward, the second nozzle being provided in the air-current generating device.
 4. The sheet feeding device according to claim 2, wherein the sheet feeding device is configured to convey the uppermost sheet, wherein the sheet feeding device is located above the sheet storage unit, wherein the second air current changes a direction thereof as the second air current hits an endless sheet feeding belt or the uppermost sheet that is sucked to the endless sheet feeding belt.
 5. An image forming apparatus comprising: the sheet feeding device according to claim 1; and an image forming unit that forms an image on the sheet. 